--> Abstract: Deformation Style along the San Gregorio Fault Zone, Northern Monterey Bay, by S. D. Lewis; #90920 (1999).

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Department of Geology, California State University, Fresno, CA 93740

Abstract: Deformation Style along the San Gregorio Fault Zone, Northern Monterey Bay

A regional grid of Common Depth Point seismic reflection profiles acquired by industry and by the USGS provides the basis for mapping three zones of active folding and thrust faulting beneath the continental shelf and slope in the northern part of the Monterey Bay National Marine Sanctuary. One zone, beneath the inner continental shelf, is composed of a well-developed imbricate fan of landward-dipping faults with associated folds in the sediment section of the Outer Santa Cruz Basin. The San Gregorio fault zone appears to comprise the landward boundary of this zone. The San Gregorio fault zone is currently seismically active, suggesting that the seaward portion of the foldand-thrust system is also active. A second zone of thrust faults extends for about 75 km along the seaward edge of the continental shelf, but appears to be seismically quiet. A third zone of thrust faulting is present at the base of the continental slope north of Monterey Canyon. This zone of faulting has produced localized uplift and doming of the seafloor, and is associated with low level seismicity.

These structures may accommodate westward relative motion of the Santa Cruz Mountains around the bend of the San Andreas fault in the region of Loma Prieta. Alternatively, the small component of Pacific-North America relative motion perpendicular to the trend of the San Andreas fault may be driving this deformation.

AAPG Search and Discovery Article #90920©1999 AAPG Pacific Section Meeting, Monterey, California